1. Field of the Invention
This invention relates to a motor vehicle comprising two driven axles, one of which is adapted to be disconnected from the drive means by means of a disconnecting clutch, which is adapted to be automatically disengaged by clutch control means in response to a brake application.
2. Description of the Prior Art
Motor vehicles having a continuously driven axle and a second driven axle, which is arbitrarily operable by means of a control device, are known in various forms but have the disadvantage that a brake application during an all-wheel drive operation may result in an unstable handling of the vehicle, particularly when the wheels on the two sides of the vehicle are rolling on paths having different coefficients of friction. Such unfavorable handling is due to the fact that the two axles are then coupled to each other so that the distribution of the braking force to the wheels of the two axles differs from the required distribution. It will be understood that such stability losses will mainly occur when the vehicle is being strongly or suddenly braked from a high speed of travel during all-wheel operation.
It is also known (Published German Application 33 17 247) that during an operation in which both axles are driven one axle can be disconnected from the motor by a disconnecting clutch, which is automatically disengageable in response to a brake application. The disconnecting clutch consists of an overrunning clutch, which has various disadvantages. When the overrunning clutch has been disengaged to disconnect one axle from the drive when the vehicle is coasting, only the other axle will be available for the braking by the drag torque of the engine. For a reverse travel with both axles driven, the overrunning clutch must be bridged. Besides, such overrunning clutch has a comparatively complicated structure, particularly because it must be bridged for a reverse travel with both axles driven.